Certain N-substituted butyramide derivatives
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 806,061 filed Dec. 6, 1985. 
    
    
     SUMMARY OF THE DISCLOSURE 
     The present invention concerns and has for its object new butyramide derivatives corresponding to Formula ##STR2## wherein X and Y independently represent hydroxymethyl; cyano; carboxy; functionally modified carboxy selected from esterified carboxy, carbamoyl, and N-substituted carbamoyl; 5-tetrazolyl; 2-oxazolyl, 4,5-dihydro-2-oxazolyl, or each said grouping substituted by lower alkyl; R and R o  independently represent lower alkyl, (C 3  -C 7 )-cycloalkyl-lower alkyl, or aryl-lower alkyl; A represents methylene; or A represents methylene substituted by lower alkyl, by lower alkylthio-lower alkyl, by aryl-lower alkylthio-lower alkyl, by arylthio-lower alkyl, by hydroxy-lower alkyl, by acyloxy-lower alkyl, by lower alkoxy-lower alkyl, by aryl-lower alkyloxy-lower alkyl, by aryloxy-lower alkyl, by amino-lower alkyl, by acylamino-lower alkyl, by guanidino-lower alkyl, by (C 3  -C 7 )-cyclo-alkyl, by (C 3  -C 7 )-cycloalkyl-lower alkyl, by aryl or aryl-lower alkyl; pharmaceutically acceptable ester and amide derivatives of any said compounds having a free carboxy group; pharmaceutically acceptable salts of any said compounds with a salt-forming group; their pharmaceutical compositions; methods for their preparation; and their use as pharmaceutical agents, e.g. as endopeptidase enzyme inhibitors in mammals. 
     The compounds of the invention exhibit valuable pharmacological properties, particularly by virtue of their ability to inhibit metallo-endopeptidase enzymes, such as the enkephalin degrading enzyme enkephalinase. 
     The foregoing attributes render the N-substituted butyramide derivatives of this invention particularly useful when administered, alone or in combination, to mammals e.g. for the treatment of conditions. responsive to e.g. the inhibition of enkephalinase, namely as analgesic, anticonvulsant, psychotropic (particularly antidepressant and neuroleptic), cardiovascular (particularly antihypertensive and diuretic), and antiinflammatory agents. 
     Compounds of formula I, depending on the nature of R, R o , X, Y and A possess a number of asymmetric carbon atoms. The resulting diastereoisomers and optical antipodes are encompassed by the instant invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     More specifically, the instant invention relates to compounds of formula II, namely the glutaric acid derivatives ##STR3## wherein R 1  and R 2  independently represent lower alkyl, (C 3  -C 7 )-cycloalkyl-lower alkyl, or aryl-lower alkyl; A represents methylene; or A represents methylene substituted by lower alkyl, by lower alkylthio-lower alkyl, by hydroxy-lower alkyl, by acyloxy-lower alkyl, by lower alkoxy-lower alkyl, by aryl-lower alkylthio-lower alkyl, by aryl-lower alkyloxy-lower alkyl, by aryloxy-lower alkyl, by arylthio-lower alkyl, by amino-lower alkyl, by acylamino-lower alkyl, by guanidino-lower alkyl, by (C 3  -C 7 )-cycloalkyl-lower alkyl or by aryl-lower alkyl; a mono- or bis-carboxylic acid derivative thereof in which the derivative is selected from an unsubstituted amide or mono- or di-(C 1  -C 20 )-alkylamide; a tertiary lower alkylene, oxalkylene or azaalkylene amide wherein the lower alkylene, oxalkylene or azaalkylene group together with the amide nitrogen forms a 5-, 6- or 7-membered ring, or said lower alkylene, oxalkylene or azaalkylene amide is substituted on the ring by lower alkyl, hydroxy-(lower)alkyl or by lower alkanoyloxy-(lower) alkyl; an arylamide; an aryl-lower alkylamide; an (amino or acylamino)-(lower)alkylamide; a C.sub. -C 20  -alkyl ester; an (amino, acylamino, mono- or di-lower alkylamino, carboxy or lower carboalkoxy)-substituted lower alkyl ester; an aryl-(lower) alkyl ester; a lower alkanoyloxy-(lower) alkyl ester; a 3-phthalidyl or (lower alkyl, lower alkoxy or halo)-substituted 3-phthalidyl ester; a (hydroxy, lower alkanoyloxy or lower alkoxy)-substituted (lower) alkoxymethyl ester; a bicycloalkyloxycarbonyl-lower alkyl ester; a hydroxyamide; a lower alkylsulfonylamide; a 1-(lower alkoxycarbonyloxy)-lower alkyl ester; a 3-cholestanyl or 3-cholestenyl ester; a monosaccharidyl or protected monosaccharidyl ester being an ester incorporating as the alcohol portion a monosaccharide or protected monosaccharide, e.g. a free or protected aldopentose or aldohexose in straight chain or cyclic form, e.g., furanose or pyranose form, or a free or protected glyconic acid of 5 or 6 carbon atoms or a lactone thereof; a polyhydroxy-lower alkyl or protected polyhydroxy-lower alkyl ester being an ester incorporating as the alcohol portion a polyhydroxy-lower alkane or protected polyhydroxy-lower alkane, e.g. a free or protected glycerol or erythritol; and pharmaceutically acceptable salts of any said compound with a salt forming group. 
     More particularly, the instant invention relates to the compounds of formula III ##STR4## wherein R 1  &#39; and R 2  &#39; independently represent aryl-(C.sub. -C 4 )-alkyl in which aryl represents phenyl or phenyl mono- or di-substituted by halogen, lower alkyl, hydroxy, lower alkoxy, trifluoromethyl or cyano; A represents methylene monosubstituted by lower alkyl, by phenyl-lower alkyl, by (halo, lower alkyl, hydroxy, trifluoromethyl or lower alkoxy)-mono- or disubstituted phenyl-lower alkyl, by lower alkylthio-lower alkyl, by hydroxy-lower alkyl, by lower alkoxy-lower alkyl, by amino-lower alkyl, by acylamino-lower alkyl, by guanidino-lower alkyl, by aryl-(lower alkylthio-lower alkyl or lower alkyloxy-lower alkyl) in which aryl represents indolyl, pyridyl, phenyl, or phenyl mono- or di-substituted by halogen, lower alkyl, hydroxy, lower alkoxy, trifluoromethyl or cyano; COR 3  and COR 4  independently represent carboxy, carboxy esterified in form of a pharmaceutically acceptable ester, carbamoyl and N-substituted carbamoyl in which R 3  and R 4  independently represent hydroxy; lower alkoxy; (amino, acylamino, mono-or di-lower alkylamino)-lower alkoxy; carboxy-lower alkoxy; lower alkoxycarbonyl-lower alkoxy; aryl-lower alkoxy in which aryl represents optionally (halogen, lower alkyl, hydroxy or lower alkoxy)-mono- or di-substituted phenyl or pyridyl; (hydroxy, lower alkanoyloxy or lower alkoxy)-lower alkoxy; (hydroxy, lower alkanoyloxy or lower alkoxy)-lower alkoxymethoxy; bicyclo[2,2,1]-heptyloxycarbonyl-lower alkoxy; cholestan-3-oxy or cholest-5-en-3-oxy; 3-phthalidoxy or (lower alkyl, lower alkoxy or halo)-substituted 3-phthalidoxy; monosaccharidyloxy or protected monosaccharidyloxy representing e.g. glucosyloxy, galactosyloxy, mannosyloxy, sorbosyloxy, allosyloxy, ribosyloxy, arabinosyloxy, ribonyloxy, gluconyloxy, or cyclic, e.g. appropriate pyranose, furanose or lactone forms thereof, wherein hydroxy groups are free or one or more, as appropriate, are protected in form of esters, e.g. a lower alkanoyl or a benzoyl ester, in form of ethers, e.g. a lower alkyl or benzyl ether, or, in case two vicinal hydroxy groups are involved, in the form of acetals or ketals, e.g. a lower alkylidene, a benzylidene or a 5-or-6-membered cycloalkylidene derivative; polyhydroxy-lower alkoxy or protected polyhydroxy-lower alkoxy representing, e.g., dihydroxypropyloxy or trihydroxy- butyloxy wherein hydroxy groups are free or one or more, as appropriate, are protected in form of esters, e.g., a lower alkanoyl or a benzoyl ester, in form of ethers, e.g. a lower alkyl or benzyl ether, or, in case two vicinal hydroxy groups are involved, in the form of acetals or ketals, e.g. a lower alkylidene, a benzylidene or a 5-or-6- membered cycloalkylidene derivative; 1-(lower alkoxycarbonyloxy)-lower alkoxy; amino; mono- or di-(lower alkylamino; morpholino; N-lower alkylpiperazino; pyrrolidino; piperidino; perhydroazepino; (amino or lower alkanoyl amino)-lower alkylamino; hydroxyamino; or lower alkylsulfonylamino; and pharmaceutically acceptable salts of any said compounds with a salt forming group. 
     Any pharmaceutically acceptable prodrug derivatives, e.g. any pharmaceutically acceptable mono- or di-esters and amides of the di-carboxylic acids of this invention that may be convertible by solvolysis or under physiological conditions to the carboxylic acids e.g. esters and amides cited herein, represent a particular object of the invention. Preferred as pharmaceutically acceptable prodrug derivatives are the pharmaceutically acceptable mono- or di-esters of said carboxylic acids as defined herein. 
     Said esters are preferably, e.g., the straight chain or branched alkyl, the pivaloyloxymethyl, bornyloxycarbonylmethyl, benzyl, pyridylmethyl, alpha-carboxyethyl, esterified alpha-carboxyethyl, 1-(lower alkoxycarbonyloxy)-lower alkyl, 3-phthalidyl, cholestan-3-yl or cholest-5-en-3-yl esters; the monosaccharidyl or protected monosaccharidyl esters being esters incorporating as the alcohol portion a monosaccharide or protected monosaccharide, e.g. a free or protected aldopentose or aldohexose in straight chain or cyclic form, e.g., furanose or pyranose form, or a free or protected glyconic acid of 5 or 6 carbon atoms or a lactone thereof; the polyhydroxy-lower alkyl or protected polyhydroxy-lower alkyl esters being esters incorporating as the alcohol portion a polyhydroxy-lower alkane or protected polyhydroxy-lower alkane, e.g. a free or protected glycerol or erythritol; 
     Preferred are the compounds of formula III wherein R 1  &#39; and R 2  &#39; independently represent aryl-(C 1  -C 4 )-alkyl in which aryl represents phenyl or phenyl mono- or di-substituted by halogen, lower alkyl, hydroxy, lower alkoxy or trifluoromethyl; A represents methylene substituted by lower alkyl, by phenyl-lower alkyl, by lower alkylthio-lower alkyl, by lower alkyloxy-lower alkyl, by phenyl-(lower alkylthio-lower alkyl or lower alkyloxy-lower alkyl), by pyridyl-(lower alkylthio-lower alkyl or lower alkyloxy-lower alkyl), by amino-lower alkyl, by acylamino-lower alkyl or by guanidino-lower alkyl; R 3  and R 4  independently represent hydroxy; lower alkoxy; (amino, mono- or di-lower alkylamino)-lower alkoxy; alpha-carboxy-lower alkoxy; alpha-lower alkoxycarbonyl-lower alkoxy; aryl-methoxy in which aryl represents phenyl, pyridyl, or (halogen, lower alkyl or lower alkoxy)-monosubstituted phenyl or pyridyl; (lower alkanoyloxy or lower alkoxy)-methoxy; (hydroxy, lower alkanoyloxy or lower alkoxy)-ethoxymethoxy; bicyclo[2,2,1]heptyloxycarbonylmethoxy; 1-(lower alkoxycarbonyloxy)-lower alkoxy; 3-phthalidoxy or (lower alkyl, lower alkoxy or halogen)-substituted 3-phthalidoxy; cholestan-3-oxy or cholest-5-en-3-oxy; monosaccharidyloxy or protected monosaccharidyloxy selected from glucosyloxy, galactosyloxy, mannosyloxy, sorbosyloxy, allosyloxy, ribosyloxy, arabinosyloxy, ribonyloxy, gluconyloxy, or cyclic, e.g. appropriate pyranose, furanose or lactone forms thereof, wherein hydroxy groups are free or one or more, as appropriate, are protected in form of a lower alkanoyl or a benzoyl ester, in form of a lower alkyl or benzyl ether, or, in case two vicinal hydroxy groups are involved, in the form of a lower alkylidene, a benzylidene or a 5-or-6-membered cycloalkylidene derivative; polyhydroxy-lower alkoxy or protected polyhydroxy-lower alkoxy selected from dihydroxypropyloxy or trihydroxybutyloxy wherein hydroxy groups are free or one or more, as appropriate, are protected in form of a lower alkanoyl or a benzoyl ester, in form of a lower alkyl or benzyl ether, or, in case two vicinal hydroxy groups are involved, in the form of a lower alkylidene, a benzylidene or a 5-or 6-membered cycloalkylidene derivative; amino; mono- or di-lower alkylamino; morpholino; N-methylpiperazino; piperidino; perhydroazepino; amino-lower alkylamino; (aryl or aryl-lower alkyl)-amino in which aryl represents pyridyl, phenyl or phenyl substituted by lower alkyl, halogen or trifluoromethyl; or lower alkylsulfonylamino; and pharmaceutically acceptable salts of any said compounds with a basic or acidic salt forming group. 
     Further preferred are the above compounds of formula III wherein R 3  and R 4  independently represent hydroxy; lower alkoxy; pivaloyloxymethoxy; bornyloxycarbonylmethoxy; benzyloxy; pyridylmethoxy; alpha-carboxyethoxy; alpha-lower alkoxycarbonylethoxy; 3-phthalidoxy; monosaccharidyloxy or protected monosaccharidyloxy selected from glucofuranosyloxy, glucopyranosyloxy, galactopyranosyloxy, allofuranosyloxy, mannofuranosyloxy, ribofuranosyloxy, sorbofuranosyloxy, arabinofuranosyloxy and ribono(1,4-lactone)-yloxy, wherein hydroxy groups are free or hydroxy groups are protected in form of a lower alkanoyl ester, in form of a benzyl ether or in form of an isopropylidene, a benzylidene or cyclohexylidene derivative; amino, mono- or di-lower alkylamino; morpholino; or lower alkylsulfonylamino; and pharmaceutically acceptable salts of any said compounds with a basic or acid salt forming group. 
     Particularly preferred are the compounds of formula III wherein R 1  &#39;, R 2  &#39; and A have meaning as defined above; COR 3  and COR 4  represent carboxy or carboxy esterified in form of a pharmaceutically acceptable ester wherein R 3  and R 4  independently represent hydroxy, lower alkoxy, benzyloxy, pyridylmethoxy, pivaloyloxymethoxy, 3-phthalidoxy, monosaccharidyloxy or protected monosaccharidyloxy as defined above. 
     Especially preferred are the above compounds of formula III wherein one of R 3  and R 4  represents hydroxy and the other of R 3  and R 4  represents lower alkoxy, pivaloyloxymethoxy, or protected monosaccharidyloxy. 
     A specific embodiment of the invention is represented by the glutaric acid derivatives of formula IV ##STR5## wherein m and n independently represent an integer from 1 to 4; R 3  &#39; and R 4  &#39; represent hydroxy; R 5  and R 6  independently represent hydrogen, halogen, hydroxy, lower alkoxy, lower alkyl or trifluoromethyl; R 7  represents lower alkyl, aryl-C.sub. -C 4  -alkyl, (C 5  -C 7 )-cycloalkyl-C 1  -C 4  -alkyl, amino-C 1  -C 4  -alkyl, hydroxy-C 1  -C 4  -alkyl, guanidino-C 1  -C 4  -alkyl, C 1  -C 4  -alkylthio-C 1  -C 4  -alkyl, C 1  -C 4  -alkyloxy-C 1  -C 4  alkyl, aryl-C 1  -C 4  -alkylthio-C 1  -C 4  -alkyl, aryl-C 1  -C 4  -alkyloxy-C 1  -C 4  -alkyl in which definitions aryl represents phenyl, pyridyl, indolyl, imidazolyl, or phenyl mono- or disubstituted by lower alkyl, hydroxy, lower alkoxy, lower alkanoyloxy, halogen or trifluoromethyl; and pharmaceutically acceptable mono- or di-ester derivatives thereof; and pharmaceutically acceptable salts of any said compounds with a free carboxy group or basic salt forming group. 
     Preferred as pharmaceutically acceptable esters of the compounds of formula IV wherein R 3  &#39; and R 4  &#39; represent hydroxy are the prodrug esters of formula IV wherein either one or both of R 3  &#39; and R 4  &#39; represent lower alkoxy of 1 to 4 carbon atoms, 3-pyridylmethoxy, benzyloxy, pivaloyloxymethoxy, 3-phthalidoxy, bornyloxycarbonylmethoxy, 1-(ethoxycarbonyloxy)-ethoxy or protected monosacharidyloxy; and pharmaceutically acceptable salts thereof. 
     Further preferred as prodrug pharmaceutically acceptable ester derivatives of the compounds of formula IV wherein R 3  &#39; and R 4  &#39; represent hydroxy are the monosaccharidyl esters wherein one of R 3  &#39; and R 4  &#39; represents protected monosaccharidyloxy, preferably 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yloxy, 1,2:3,4-di-O-isopropylidene-D-galactopyranos-6-yloxy, 2,3-0-isopropylidene-D-ribono-(1,4-lactone)-5-yloxy, 2,3:5,6-di-O-cyclohexylidene-D-mannofuranos-1-yloxy, 2,3-O-cyclohexylidene-D-ribono-(1,4-lactone)-5-yloxy, 1-methyl-2,3-O-isopropylidene-D-ribofuranos-5-yloxy, 1,2-O-isopropylidene-D-glucofuranos-3-yloxy, 2,3:-4,6-di-O-isopropylidene-L-sorbofuranos-1-yloxy, 1,2:5,6-di-O-isopropylidene-D-allofuranos-3-yloxy, 2,3:5,6-di-O-isopropylidene-D-mannofuranos-1-yloxy, 2,3,5-tri-O-benzyl-D-arabofuranos-1-yloxy, 2,3,4,6-tetra-O-benzyl-D-glucopyranos-1-yloxy or 2,3-O-benzylidene-D-ribono-(1,4-lactone)-5-yloxy, and the other of R 3  &#39; and R 4  &#39; represents hydroxy, lower alkoxy of 1 to 4 carbon atoms, pyridylmethoxy, benzyloxy or pivaloyloxymethoxy. 
     Particularly preferred as prodrug pharmaceutically acceptable ester derivatives of the compounds of formula IV wherein R 3  &#39; and R 4  &#39; represent hydroxy are the esters wherein either one or both of R 3  &#39;0 and R 4  &#39; represent lower alkoxy of 1 to 4 carbon atoms, 3-pyiidylmethoxy, benzyloxy, pivaloyloxymethoxy, 3-phthalidoxy, bornyloxycarbonylmethoxy, 1-(ethoxycarbonyloxy)-ethoxy, or amino; and pharmaceutically acceptable salts thereof. 
     Preferred are the compounds of formula IV wherein m and n represent the integer 1; R 3  &#39; and R 4  &#39; independently represent hydroxy, lower alkoxy, pivaloyloxymethoxy, pyridylmethoxy, benzyloxy, 3-phthalidoxy, or protected monosaccharidyloxy as defined above; R 5  and R 6  represent hydrogen; and R 7  represents amino-C 1  -C 4  -alkyl, guanidino-C 1  -C 4  -alkyl, phenyl-C 1  -C 4  -alkyl, phenyl-C 1  -C 4  -alkylthio-C 1  -C 4  -alkyl, phenyl-C 1  -C 4  -alkyloxy-C 1  -C 4  -alkyl, pyridyl-C 1  -C 4  -alkyl, pyridyl-C 1  -C 4  -alkylthio-C 1  -C 4  alkyl or pyridyl-C 1  -C 4  -alkyloxy-C 1  -C 4  -alkyl; and pharmaceutically acceptable salts of any said compounds with a free carboxy group or basic salt forming group. 
     Further preferred are the compounds of formula IV wherein m and n represent the integer 1; R 3  &#39; and R 4  &#39; independently represent hydroxy, lower alkoxy, pivaloyloxymethoxy, pyridylmethoxy, benzyloxy, 3-phthalidoxy, or protected monosaccharidyloxy as defined above; R 5  and R 6  represent hydrogen; and R 7  represents phenyl-C 1  -C 4  -alkyl, phenyl-C 1  -C 4  -alkylthio-C 1  -C 4  -alkyl, phenyl-C 1  -C 4  -alkyloxy-C 1  -C 4  -alkyl, pyridyl-C 1  -C 4  -alkyl, pyridyl-C 1  -C 4  -alkylthio-C 1  -C 4  alkyl or pyridyl-C 1  -C 4  -alkyloxy-C 1  -C 4  -alkyl; and pharmaceutically acceptable salts of any said compounds with a free carboxy group or basic salt forming group. 
     The compounds of the invention, of formula I-IV and derivatives may contain several asymmetric carbon atoms, depending on the nature of the substituents. 
     Thus the compounds of the invention exist in the form of stereoisomers, e.g., racemates, pure enantiomers, or mixtures thereof, all of which are within the scope of the invention. 
     The compounds of the invention, those of formula I, may exist in different isomeric forms, e.g. wherein the asymmetric carbon atoms within group A and on the chain bearing the R and R o  groups may exist either in the S or R configuration. 
     For example, in the compounds of formula II and functional derivatives thereof wherein the linking group A represents substituted methylene, said asymmetric carbon atom linking the NH and CO groupings of the alpha-amino-acid involved is preferably in the configuration corresponding to that of the (L)-alpha-aminoacid. Except for the compounds which are (L)-cysteine derivatives, the asymmetric carbon involved is in the (S)-configuration; it is in the (R)-configuration in the case of cysteine derivatives. 
     Furthermore, in said compounds of formula II and derivatives thereof, the glutaryl chain, by virtue of the two asymmetric carbon atoms bearing the R 1  and R 2  substituents, exists as two distinct racemic diastereoisomeric forms which may be called erythro and threo depending on the relative orientation of the R 1  and R 2  substituents on the chain. Each of the two racemates with respect to the gluraryl chain consists of the optically active enantiomers (or antipodes) having the (S,S), (R,R) and (R,S), (S,R) configurations, respectively. 
     Preferred is the threo racemic form and particularly the enantiomeric form thereof depicted in formula IIa ##STR6## and wherein A, R 1  and R 2  have meaning as defined herein above for compounds of formula II. 
     For the glutaric acid derivatives of formula III and IV, the glutaryl chain likewise exists in two distinct disatereomeric forms which may be called erythro and threo respectively. Preferred are e.g. the compounds of formula IV wherein the glutaryl chain is in the threo diastereoisomeric form, more particularly the compounds having the stereochemistry as depicted in formula IVa. ##STR7## wherein R 3  &#39;, R 4  &#39;, R 5 , R 6 , R 7 , m and n have meaning as defined hereinabove for compounds of formula IV. 
     Illustrative thereof, in the above compounds of formula IVa wherein m and n represent the integer 1, each of the two carbon atoms on the glutaryl chain carrying said substituent is assigned the (S)-configuration; in said compounds of formula IVa wherein m and n represent an integer from 2 to 4, each of the two carbon atoms is assigned the (R)-configuration. The configuration at carbon atom bearing R 7  corresponds to the configuration of the (L)-alpha-aminoacid involved. 
     The general definitions used herein unless denoted otherwise have the following meanings within the scope of the present invention. 
     Aryl represents a carbocyclic or heterocyclic aromatic radical preferably being phenyl, thienyl, biphenyl, indolyl, pyridyl, imidazolyl, naphthyl, furyl, each optionally substituted; aryl advantageously represents optionally substituted phenyl or pyridyl. 
     Optionally substituted phenyl represents preferably phenyl or phenyl substituted by one to three substituents, advantageously by lower alkyl, hydroxy lower alkoxy, lower alkanoyloxy, halogen, cyano or trifluoromethyl. 
     Optionally substituted pyridyl represents 2-, 3- or 4-pyridyl or 2-, 3- or 4-pyridyl preferably substituted by lower alkyl, halogen or cyano. 
     Optionally substituted thienyl represents 2- or 3-thienyl or 2- or 3-thienyl preferably substituted by lower alkyl. 
     Optionally substituted indolyl represents preferably 2- or 3-indolyl or 2- or 3-indolyl preferably substituted by lower alkyl, halogen or lower alkoxy. 
     Optionally substituted naphthyl represents 1- or 2-naphthyl or 1- or 2-naphthyl preferably substituted by lower alkyl, lower alkoxy or halogen. 
     Optionally substituted furyl represents 2- or 3-furyl or 2- or 3-furyl preferably substituted by lower alkyl. 
     Optionally substituted imidazolyl is preferably 1- or 2-imidazolyl or 1- or 2-imidazolyl preferably substituted by lower alkyl. 
     Aryl, as in arylamide and aryl-lower alkyl ester, is preferably optionally substituted phenyl or optionally substituted pyridyl. 
     Aryl, as in aryl-lower alkyl, aryloxy, arylthio is preferably phenyl or phenyl substituted by one or two of lower alkyl, lower alkoxy, hydroxy, lower alkanoyloxy, halogen, trifluoromethyl or cyano; and aryl-lower alkyl is advantageously benzyl or phenethyl optionally substituted by one or two of lower alkyl, lower alkoxy, hydroxy, lower alkanoyloxy, halogen or trifluoromethyl. 
     C 1  -C 20  Alkyl represents branched or unbranched alkyl with 1 to 20 carbon atoms. 
     The term cycloalkyl represents a saturated cyclic hydrocarbon radical which preferably contains 3 to 7 ring carbons and is, preferably, cyclopentyl or cyclohexyl. 
     The term cycloalkyl(lower)alkyl represents preferably 1- or 2-(cyclopentyl or cyclohexyl)ethyl, 1-, 2- or 3-(cyclopentyl or cyclohexyl)propyl, or 1-, 2-, 3- or 4-(cyclopentyl or cyclohexyl)-butyl. 
     The term &#34;lower&#34; referred to above and hereinafter in connection with organic radicals or compounds respectively defines such with up to and including 7, preferably up and including 4 and advantageously one or two carbon atoms. 
     A lower alkyl group preferably contains 1-4 carbon atoms and represents for example ethyl, propyl, butyl or advantageously methyl. 
     A lower alkoxy group preferably contains 1-4 carbon atoms and represents for example methoxy, propoxy, isopropoxy or advantageously ethoxy. 
     A mono-lower alkylamino group preferably contains 1-4 carbon atoms in the alkyl portion and is for example N-methylamino, N-propylamino or advantageously N-ethylamino. 
     A di-lower alkylamino group preferably contains 1-4 carbon atoms in each lower alkyl portion and represents, for example, N,N-dimethylamino, N-methyl-N-ethylamino and advantageously N,N-diethylamino. 
     A lower alkoxycarbonyl group preferably contains 1 to 4 carbon atoms in the alkoxy portion and represents, for example, methoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl or advantageously ethoxycarbonyl. 
     Aryl-lower-alkoxy represents advantageously e.g. benzyloxy, benzyloxy substituted by methyl, methoxy or chloro, and pyridylmethoxy. 
     Pyridyl represents 2-, 3- or 4-pyridyl. 
     Carboxy-lower alkoxy represents advantageously e.g. 1-carboxyethoxy. 
     Lower alkoxycarbonyl-lower alkoxy represents advantageously e.g. 1-(ethoxycarbonyl)ethoxy. 
     Amino-lower alkoxy, mono-lower alkylamino-lower alkoxy, di-(lower)alkylamino-lower alkoxy advantageously represent respectively e.g. aminoethoxy, ethylaminoethoxy, diethylaminoethoxy. 
     Hydroxy-lower alkyl is preferably hydroxymethyl, hydroxyethyl or hydroxypropyl, advantageously hydroxymethyl. 
     Bicycloalkyloxycarbonyl-lower alkoxy preferably represents bicyclo[2,2,1]heptyloxycarbonyl-lower alkoxy unsubstituted or substituted by lower alkyl, advantageously bornyloxycarbonylmethoxy. 
     Amino-lower alkyl represents preferably amino-(ethyl, propyl or butyl), particularly omega-amino-(ethyl, propyl or butyl). 
     Guanidino-lower alkyl represents preferably guanidino-(ethyl, propyl or butyl), and particularly omega-guanidino-(ethyl, propyl or butyl). 
     Lower alkylidene is preferably isopropylidene. 
     Cycloalkylidene is preferably cyclohexylidene. 
     Halogen preferably represents chlorine, but may also be bromine, fluorine or iodine. 
     Lower alkanoyl is preferably acetyl, propionyl, butyryl, or pivaloyl. 
     Acyl in acyloxy, acyloxy-lower alkyl, acylamino, acylamino-lower alkyl represents preferably lower alkanoyl, aroyl, lower alkoxycarbonyl or aryl-lower alkoxycarbonyl advantageously lower alkanoyl. 
     Aroyl is preferably benzoyl; benzoyl substituted by one to three of lower alkyl, lower alkoxy, halogen or trifluoromethyl; thienoyl; pyrroloyl; or pyridylcarbonyl. 
     Lower alkanoyloxy is preferably acetoxy, pivaloyloxy or propionyloxy; lower alkanoylamino is preferably acet-amido or propionamido; aroyloxy is preferably benzoyloxy, or benzoyloxy substituted on the benzene ring by one to three of lower alkyl, lower alkoxy, halogen or trifluoromethyl, or hetero-aroyloxy. 
     Pyridylcarbonyl is 2-, 3- or 4-pyridyl-carbonyl, advantageously nicotinoyl. 
     Acylamino represents preferably lower alkanoylamino aroylamino, or aryl-lower alkoxycarbonylamino such as benzyloxycarbonylamino. 
     Acylamino-lower alkyl represents preferably acyl-amino(ethyl, propyl or butyl). 
     Functionally modified carboxy represents esterified carboxy, carbamoyl or carbamoyl substituted on nitrogen. 
     Esterified carboxy represents preferably carboxy esterified in form of a pharmaceutically acceptable ester, advantageously an ester that may be convertible by solvolysis or under physiological conditions to the free carboxylic acid, e.g. especially optionally substituted alkoxycarbonyl in which optionally substituted lower alkoxy represents preferably C 1  -C 20  alkoxy, advantageously lower alkoxy; (amino, acylamino, mono- or di-lower alkylamino)-lower alkoxy; carboxy- lower alkoxy, e.g. alpha-carboxy-lower alkoxy; lower alkoxycarbonyl-lower alkoxy, e.g. alpha-lower alkoxycarbonyl-lower alkoxy; aryl-lower alkoxy, preferably optionally (halo, lower alkyl or lower alkoxy)-benzyloxy or pyridyl-methoxy; (hydroxy, lower alkanoyloxy or lower alkoxy)-lower alkoxy, e.g. pivaloyloxymethoxy; (hydroxy, lower alkanoyloxy or lower alkoxy)-lower alkoxymethoxy; bicycloalkoxycarbonyl-lower alkoxy, e.g. bicyclo[2,2,1]-heptyloxycarbonyl-lower alkoxy, especially bicyclo[2,2,1]-heptyloxycarbonylmethoxy such as bornyloxycarbonylmethoxy; 1-(lower alkoxycarbonyloxy)-lower alkoxy. 
     Esterified carboxy also represents 3-phthalidoxycarbonyl and (lower alkyl, lower alkoxy, or halo)-substituted 3-phthalidoxycarbonyl. 
     Esterified carboxy further represents: 
     (a) cholestan-3-oxycarbonyl or cholest-5-en-3-oxycarbonyl; 
     (b) monosaccharidyloxycarbonyl or protected monosaccharidyloxy carbonyl in which monosaccharidyloxy and protected monosaccharidyloxy represent preferably glucosyloxy, galactosyloxy, mannosyloxy, sorbosyloxy, allosyloxy, ribosyloxy, arabinosyloxy, ribonyloxy, gluconyloxy, or cyclic, e.g. appropriate pyranose, furanose or lactone forms thereof, wherein hydroxy groups are free or one or more, as appropriate, are protected in form of esters, e.g. a lower alkanoyl or a benzoyl ester, in form of ethers, e.g. a lower alkyl or benzyl ether, or, in case two vicinal hydroxy groups are involved, in the form of acetals or ketals, e.g. a lower alkylidene, a benzylidene or a 5-or-6-membered cycloalkylidene derivative; 
     (c) polyhydroxy-lower alkoxycarbonyl or protected polyhydroxy-lower alkoxycarbonyl in which polyhydroxy-lower alkoxy and protected polyhydroxy-lower alkoxy represent preferably dihydroxypropyloxy or trihydroxybutyloxy wherein hydroxy groups are free or one or more, as appropriate, are protected in form of esters, e.g., a lower alkanoyl or a benzoyl ester, in form of ethers, e.g. a lower alkyl or benzyl ether, or, in case two vicinal hydroxy groups are involved, in the form of acetals or ketals, e.g. a lower alkylidene, a benzylidene or a 5-or-6-membered cycloalkylidene derivative. 
     Protected monosaccharidyloxy represents preferably 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yloxy, 1,2:3,4-di-O-isopropylidene-D-galactopyranos-6-yloxy, 2,3-O-isopropylidiene-D-ribono-(1,4-lactone)-5-yloxy, 2,3:5,6-di-O-cyclohexylidene-D-manno-furanos-1-yloxy, 2,3-O-cyclohexylidene-D-ribono-(1,4-lactone)-5-yloxy, 1-methyl-2,3-O-isopropylidene-D-ribofuranos-5yloxy, 1,2-O-isopropylidine-D-gluocofuranos-3-yloxy, 2,3:4,6-di-O-isopropylidene-L-sorbofuranos-1-yloxy, 1,2:5,6-di-O-isopropylidene-D-allofuranos-3-yloxy, 2,3:5,6-di-O-isopropylidene-D-mannofuranos-1-yloxy, 2,3,5-tri-O-benzyl-D-arabofuranos-1-yloxy, 2,3,4,6-tetra-O-benzyl-D-glucopyranos-1-yloxy or 2,3-O-benzylidiene-D-ribono-(1,4-lactone)-5-yloxy. 
     Protected polyhydroxy-lower alkoxy represents preferably (2,2-dimethyl-1,3-dioxolan-4-yl)-methoxy. 
     N-substituted carbamoyl represents preferably [lower alkylamino, arylamino, di-lower alkylamino, morpholino, N-lower alkylpiperazino, pyrrolidino, piperidino, perhydroazepino, (amino or acylamino)-lower alkylamino, aryl-lower alkylamino, hydroxyamino, or lower alkylsulfonylamino]carbonyl. 
     Pharmaceutically acceptable salts are either pharmaceutically acceptable acid addition salts for any basic compounds of the invention or salts derived from pharmaceutically acceptable bases for any acidic compounds of the invention. 
     Pharmaceutically acceptable salts of basic compounds of the invention are acid addition salts, which are preferably such of therapeutically acceptable inorganic or organic acids, such as strong mineral acids, for example hydrohalic, e.g. hydrochloric or hydro-bromic acid, sulfuric, phosphoric or nitric acid; aliphatic or aromatic carboxylic or sulfonic acids, e.g. formic, acetic, propionic, succinic, glycollic, lactic, malic, tartaric, gluconic, citric, maleic, fumaric, pyruvic, phenylacetic, benzoic, 4-aminobenzoic, anthranilic, 4-hydroxybenzoic, salicylic, 4-aminosalicylic, pamoic, nicotinic, methanesulfonic, ethanesulfonic, hydroxyethanesulfonic, benzenesulfonic, p-toluenesulfonic, naphthalenesulfonic, sulfanilic, cyclohexylsulfamic acid; or ascorbic acid. 
     Pharmaceutically acceptable salts of the acidic compounds of the invention, e.g. those having a free carboxy group are salts formed with pharmaceutically acceptable bases, such as alkali metal, alkaline earth metal, ammonia, mono-, di- or tri-lower (alkyl or hydroxy-alkyl)-amines, monocyclic amines or alkylenediamines, are e.g. sodium, potassium, magnesium, calcium, ammonium, mono-, di- or tri-(methyl, ethyl or hydroxyethyl)-ammonium or ethylenediammonium salts. 
     The novel compounds of the invention are pharmacologically potent endopeptidase enzyme inhibitors, e.g. enkephalinase inhibitors. The compounds inhibit the degradation of endogenous enkephalins, e.g. met-enkephalin and leu-enkephalin, by the enzyme enkephalinase in mammals. They also potentiate the diuretic and natriuretic effect of exogenous atrial natriuretic factor (ANF) in mammals. 
     The compounds of the invention are thus useful in mammals e.g. as analgesic, diuretic or antihypertensive agents for the treatment of pain or hypertension. 
     The above-cited properties are demonstrable in vitro and in vivo tests, using advantageously mammals, e.g. mice, rats, dogs, monkeys or isolated organs, tissues and preparations thereof. Said compounds can be applied in vitro in the form of solutions, e.g. preferably aqueous solutions, and in vivo either enterally, parenterally, advantageously intravenously, or intracerebroventricularly, e.g. as a suspension or in aqueous solution. The dosage in vitro may range between about 10 -4  molar and 10 -9  molar concentrations. The dosage in vivo may range depending on the route of administration, between about 0.01 and 50 mg/kg, advantageously between about 0.10 and 25 mg/kg. 
     The analgesic activity can be determined by measuring the potentiation of the analgesic effects of enkephalin and derivatives thereof, and by classical analgesic tests, such as the phenyl-p-benzoquinone induced writing test [J. Pharmacol. Exp. Therap. 125, 237 (1959)]and the hot plate test in the mouse [J. Pharmacol. Exp. Therap. 107, 385 (1953). 
     The antihypertensive activity can be determined in the spontaneously hypertensive rat, Goldblatt rat or Goldblatt dog by direct measurement of blood pressure. Advantageously, the effect is measured in the DOCA-salt hypertensive rat and/or renal hypertensive rat or dog model. 
     The diuretic (saluretic) activity can be determined in standard diuretic screens, e.g. as described in &#34;New Antihypertensive Drugs&#34;, Spectrum Publications, 1976, pages 307-321. 
     The enkephalinase inhibitory activity is determined in vitro by an adaptation of the method of Alstein et al. as described in Life Sciences 28, 185 (1981), as follows: 
     A mixture of a solution of the test compound in distilled water or distilled water and ethanol diluted with pH 6.5 buffer and of a synaptic membrane preparation from rat striatum is incubated at pH 6.5 with  3  H-Leu-enkephalin for 15 minutes at 30° C., in the presence of 10 -6  M Bestatin (to inhibit aminopeptidase activity). The reaction is stopped by the addition of 30% acetic acid and the reaction product  3  H-Tyr-gly-gly is separated from unreacted  3  H-Leu-enkephalin on a Porapak O column followed by a Cu ++-chelex  column. The  3  H-Tyr-gly-gly is counted by liquid scintillation. The amount of  3  H-Tyr-gly-gly generated in the presence of test compound as compared to control is then calculated. An IC 50  value representing the concentration of test compound required for 50% inhibition of  3  H-Tyr-gly-gly generation is then determined graphically. 
     The enkephalinase inhibitory activity can be determined in vivo, e.g. by measuring the potentiation of the analgesic activity of intracerebrally administered D-Ala 2  -met 5  -enkephalinamide or met-enkephalin in mice. The enkephalinase inhibitory activity can also be determined in vivo by direct measurement of striatum enkephalinase activity in mice. 
     The analgesic activity is preferably measured by the hot-plate test method in the mouse as follows and essentially as described in J. Pharmacol. Exp. Therap. 107, 385 (1953). 
     The compound is administered subcutaneously, intravenously or intracerebroventricularly prior to the measurement of the response latency. Male CF 1  (Charles River) mice (20 g) are allowed food and water ad libitum up to the time of testing. The hot plate test for analgesia utilizes an apparatus with an electrically heated, thermostatically controlled copper plate (Analgesia Meter). A Plexiglas cylinder, 25.5 cm x 16 cm (inner diameter) and open at both ends, confines the mice to the central area of the hot plate. The surface temperature is maintained at 55±0.5° C. Response latency is recorded as the time (seconds) from contact with the hot plate until a jump occurs or at 240 seconds if no response occurs within this time. Animals are individually tested at 15 minutes following intravenous or intracerebroventricular (ICV) injection, or 30 minutes following subcutaneous administration. Intracerebroventricular injections into the lateral ventricle are carried out according to the method of Haley and McCormick, as described in Brit. J. Pharmacol. 12; 12, 1957. 
     The mean response latency and standard error are calculated. Significance is determined using Student&#39;s unpaired t-test, 2-tailed comparison. The test agent is considered to have analgesic activity if the mean response latency is significantly higher than that of the vehicle-treated control group. The dose of test compound which significantly increases the mean response latency represents an effective analgesic dose. 
     Illustrative of the invention, N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-O-benzyl-(L)-serine has an IC 50  for inhibition of enkephalinase of about 4×10 -9  N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-homophenylalanine has an IC 50  of about 5×10 -9  M, and N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-S-benzyl-(L)-cysteine has an IC 50  of about 6×10 -9  M. 
     Accordingly the compounds are valuable pharmacological agents, particularly as endopeptidase (enkephalinase) inhibitors in mammals, especially for relieving pain and hypertension in mammals. The compounds of the invention are also useful in the preparation of corresponding pharmaceutical compositions. 
     The compounds of the invention of formula I are prepared using the following process which comprises: condensing a compound of formula V 
     
         NH.sub.2 --A--X                                            (V) 
    
     wherein A and X have meaning as defined above, in temporarily protected form if required; with a compound of formula VI ##STR8## or a reactive functional derivative thereof, wherein R, R o  and Y have meaning as defined above, in temporarily protected form if required; and, if temporarily protecting any interfering reactive group(s), removing said protecting group(s), and then isolating the resulting compound of the invention; and, if desired, converting a resulting compound of the invention into another compound of the invention, and/or, if desired, converting a resulting free compound into a salt or a resulting salt into the free compound or into another salt, and/or, if desired, separating a mixture of isomers or racemates obtained into the single isomers or racemates, and/or, if desired, resolving a racemate obtained into the optical antipodes. 
     In starting compounds and intermediates which are converted to the compounds of the invention in a manner described herein, functional groups present, such as carboxy, amino and hydroxy groups, are optionally protected by conventional protecting groups that are common in preparative organic chemistry. Protected carboxy, amino and hydroxy groups are those that can be converted under mild conditions into free carboxy, amino and hydroxy groups without other undesired side reactions taking place. 
     The purpose of introducing protecting groups is to protect the functional groups from undesired reactions with reaction components and under the conditions used for carrying out a desired chemical transformation. The need and choice of protecting groups for a particular reaction is known to those skilled in the art and depends on the nature of the functional group to be protected (carboxy group, amino group etc.), the structure and stability of the molecule of which the substituent is a part, and the reaction conditions. 
     Well-known protecting groups that meet these conditions and their introduction and removal are described, for example, in J. F. W. McOmie, &#34;Protective Groups in Organic Chemistry&#34;, Plenum Press, London, New York 1973, T.W. Greene, &#34;Protective Groups in Organic Synthesis&#34;, Wiley, New York 1984, and also in &#34;The Peptides&#34;, Vol. I, Schroeder and Luebke, Academic Press, London, New York 1965. 
     The condensation of an amine of formula V with the acid of formula VI, or a functional reactive derivative thereof, is carried out by methodology well-known in the art. 
     Reactive functional derivatives of compounds of formula VI are preferably halides, mixed anhydrides such as the pivaloyl, alkoxycarbonyl or cyanoacetyl anhydride, cyclic glutaric anhydrides for compounds of formula VI where Y represents carboxy or the corresponding lactones for compounds of formula VI in which Y represents hydroxymethyl. 
     The condensation of a compound of formula V in suitably protected form depending on nature of substituents, with a compound of formula VI in the form of a free carboxylic acid is carried out advantageously in the presence of a condensing agent such as dicyclohexylcarbodiimide or 1,1&#39;-diimidazolylcarbonyl in an inert solvent such as methylene chloride, preferably at room temperature or at a temperature near the boiling point of the solvent. 
     The condensation of a compound of formula V with the anhydride, as a reactive functional derivative of a compound of formula VI wherein Y represent carboxy, is carried out in an inert solvent such as toluene or methylene chloride, advantageously in the presence of a base, e.g. an inorganic base such as potassium carbonate or an organic base such as triethylamine or pyridine, at a temperature ranging from about 0° to 100°, preferably at room temperature. 
     The condensation of a compound of formula V with a reactive functional derivative of an acid of formula VI in the form of an acid halide, advantageously an acid chloride, or mixed anhydride, is carried out in an inert solvent under conditions analogous to those described above for condensation with a glutaric acid anhydride, advantageously in the presence of a basic solvent, e.g. pyridine. 
     The starting materials of formula V are alpha-aminoacids and derivatives thereof known in the art or which may be prepared by conventional methods known in the art. 
     The starting materials of Formula VI are known, or, if new, may be prepared according to conventional methods, e.g., those illustrated by the examples herein. 
     For example, starting materials of formula VI, e.g. wherein Y represents carboxy or functionally modified carboxy, are prepared from the correspondingly substituted glutaric anhydride by hydrolysis, alcoholysis or aminolysis by methods well known in the art for opening of a cyclic anhydride. Monofunctional derivatives of a dicarboxylic acid of formula VI (wherein Y does not represent free carboxy) are converted to the corresponding reactive functional derivative, e.g. an acyl halide, by treatment with e.g. oxalyl chloride in methylene chloride. 
     The starting substituted glutaric anhydride is prepared by cyclization of the correspondingly substituted glutaric acid by treatment with e.g. acetyl chloride. 
     The substituted glutaric acids are prepared by methods well-known in the art, e.g. by condensation of the appropriately substituted di-lower alkyl malonate with an optionally alpha-substituted acrylic acid derivative or precursor thereof, e.g. as illustrared in Acta Chem. Scand. 1958, 314 for the preparation of dibenzylglutaric acid. 
     In the case of 2,4-disubstituted glutaric acids, both threo and erythro diastereoisomers are obtained and may be isolated. When both the 2- and 4-substituents are identical, the isomers consist of the racemic (d,l) threo and meso erythro isomers. The racemic (d,l) diastereoisomer can be further resolved into the individual enantiomers by methods well-known in the art. 
     The compounds of the invention so obtained, can be converted into each other according to conventional methods. Thus, for example, resulting amides or esters may be hydrolyzed with aqueous alkalies, such as alkali metal carbonates or hydroxides. Resulting free acids may be esterified with e.g. said unsubstituted or substituted alkanols or reactive esterified derivatives thereof such as alkyl halides, or diazoalkanes, or free acids are also converted into said metal, ammonium or acid addition salts in conventional manner. 
     Thus, any resulting free acid or base can be converted into a corresponding metal, ammonium or acid addition salt respectively, by reacting it with an equivalent amount of the corresponding base, basic salt, acid or ion exchange preparation, e.g. said acids with alkali or ammonium hydroxides or carbonates, or e.g. aminoalkyl esters with said inorganic or organic acids respectively. Any resulting salt may also be converted into the free compound, by liberating the latter with stronger acids or bases, respectively. In view of the close relationship between the free compounds and the salts thereof, whenever a compound of the invention, or intermediate, is referred to in this context, a corresponding salt is also intended, provided such is possible or appropriate under the circumstances. 
     The compounds, including their salts, may also be obtained in the form of their hydrates, or include other solvents used for the crystallization. 
     Furthermore, the mono or bis functional derivatives of, e.g., the dicarboxylic acids of formula II, wherein either or both carboxy groups are esterified by identical or different radicals, may be prepared by condensing a said diacid, e.g. of formula II or a mono ester derivative thereof, with an esterifying agent of the formula VII 
     
         R.sub.8 --Z                                                (VII) 
    
     wherein Z represents hydroxy or a reactive esterified hydroxyl group; and R 8  represents any of the ester radicals defined hereinabove and comprising such as alkyl, e.g. methyl, ethyl, n- or i-propyl or butyl; substituted lower alkyl e.g. omega-amino, omea-(N-methyl or N,N-dimethylamino), alpha-carboxy or omega-ethoxycarbonyl-(ethyl, propyl or butyl); aryl(lower)alkyl, e.g. benzyl, (methyl-, methoxy-, chloro-)substituted benzyl, or pyridylmethyl; lower alkanoyloxy-lower alkyl, e.g. pivaloyloxymethyl; 3-phthalidyl or (methyl-, methoxy-, chloro-)substituted 3-phthalidyl, (hydroxy-lower alkanoyloxy-, lower alkoxy-)substituted lower alkoxymethyl e.g. β-(hydroxy-, acetyloxy-, methoxy-) ethoxymethyl; unsubstituted or lower alkyl substituted bicyclo[2,2,1]heptyloxycarbonyl-(lower)-alkyl, advantageously bornyloxycarbonylmethyl; 1-(lower alkoxycarbonyloxy)-loweralkyl, e.g. 1-(methoxy-, ethoxy- or propoxy-carbonyloxy)-methyl, ethyl or propyl; protected monosaccharidyl as defined above; or protected polyhydroxyalkyl as defined above. 
     A reactive esterified hydroxyl group Z in a compound of the formula VII is a hydroxyl group esterified by a strong inorganic or organic acid. Corresponding Z groups are in particular halogen, for example chlorine, bromine or preferably iodine, also sulfonyloxy groups, such as lower alkyl- or arylsulfonyloxy groups, for example methane-, ethane-, benzene- or toluene-sulfonyloxy groups. 
     The esterification of the carboxyl groups, optionally in salt form, with a compound of formula VII wherein Z represents a reactive esterified hydroxyl group, is performed in a manner known per se, in the presence of for example an organic base, such as an organic amine, for example a tertiary amine, such as tri-lower alkylamine, for example trimethylamine, triethylamine or ethyl-di-isopro- pylamine, an N,N-di-lower-alkyl-aniline, for example N,N-di-methylaniline, a cyclic tertiary amine, such as an N-lower-alkylated morpholine, for example N-methyl-morpholine, a base of the pyridine type, for example pyridine, an inorganic base, for example hydroxides, carbonates, or hydrogen carbonates of alkali metals or alkaline-earth metals, for example sodium, potassium or calcium hydroxide, carbonate or hydrogen carbonate, or a quaternary ammonium base, such as a tetraalkylammonium hydroxide, carbonate or hydrogen carbonate, for example in which alkyl is e.g. methyl, ethyl, propyl, isopropyl, butyl, or the like, or an oxirane, for example a lower 1,2-alkylene oxide, such as ethylene oxide or propylene oxide. 
     The di-carboxylic acid, e.g. of the formula II, or a monoester thereof is preferably first converted into a salt of one of the stated organic or inorganic bases, especially into the sodium or potassium salt, and is then reacted with a compound of the formula VII. The compounds of formula VII are known or can be prepared by methods well-known to the art. 
     A compound of the formula VII wherein Z is a reactive esterified hydroxyl group can be prepared in situ. For example, a compound of the formula VII wherein Z is chloro can be converted by treatment with sodium iodide in a solvent, for example in acetone or acetonitrile, into a compound of the formula VII wherein Z is iodo; or esterification can be carried out with a chloro compound of the formula VII in the presence of sodium iodide. 
     The esterification reaction of carboxylic acids of the invention is performed in a suitable inert solvent or solvent mixture, for example in dimethylformaide, a halogenated hydrocarbon e.g. methylene chloride, carbon tetrachloride or chlorobenzene, a ketone, e.g. acetone, an ester, e.g. ethyl acetate, or a nitrile, e.g. acetonitrile, or mixtures thereof, preferably at room temperature, or if necessary at a reduced or elevated temperature, advantageously at -10° to +40° C., and/or in an inert-gas atmosphere, for example in a nitrogen atmosphere. 
     Esterification of a carboxylic acid with an alcohol of formula VII wherein Z represents hydroxy is carried out in a manner known per se, preferably in the presence of an acid catalyst e.g. sulfuric acid or boron trifluoride etherate preferably at an evelated temperature, advantageously ranging from about 40° C. to 100° C. 
     The compounds of the invention which contain a phenyl ring may be converted to the corresponding compounds of the invention containing a cyclohexyl ring, respectively. Such conversion is carried out e.g. by catalytic hydrogenation in the presence of a catalyst such as rhodium, nickel or platinum in a polar medium using procedures well-known in the art and as illustrated in the examples. 
     In case mixtures of geometrical or optical isomers of the above compounds of Formulae I to VI are obtained, these can be separated into the single isomers by methods in themselves known, e.g., by fractional distillation, crystallization and/or chromatography. Racemic products can likewise b resolved into the optical antipodes, for example, by separation of diastereomeric salts thereof, e.g., for basic compounds by the fractional crystallization of d- or 1-(tartrate, mandelate or camphorsulfonate) salts, or for acidic compounds by fractional crystallization of d- or 1-(alpha-methylbenzylamine, cinchonidine, cinchonine, quinine, quinidine, ephedrine, dehydroabietylamine, brucine or strychnine)-salts. 
     The above-mentioned reactions are carried out according to standard methods, in the presence or absence of diluents, preferably such as are inert to the reagents and are solvents thereof, of catalysts, alkaline or acidic condensing or said other agents respectively and/or inert atmospheres, at low temperatures, room temperature or elevated temperatures, preferably near the boiling point of the solvents used, at atmospheric or superatmospheric pressure. 
     The invention further includes any variant of said processes, in which an intermediate product obtainable at any stage of the process is used as a starting material and any remaining steps are carried out, or the process is discontinued at any stage discontinued at any stage threof, or in which the starting materials are formed under the reaction conditions, or in which the reaction components are used in the form of theirsalts or optically pure antipodes. Mainly those starting materials should be used in said reactions, that lead to the formation of those compounds indicated above as being preferred. For example, the compounds of formula IVa or the corresponding threo racemate, are those derived from the corresponding trans-2,4-disubstituted glutaric anhydride. 
     The present invention additionally relates to the use in mammals of the compounds of the invention and their pharmaceutically acceptable, non-toxic acid addition salts, or pharmaceutical compositions thereof, as medicaments, e.g. as enkephalinase inhibitors, e.g. for the treatment of pain or of cardiovascular disorders such as hypertension. 
     The present invention also relates to the use of the compounds of the invention for the preparation of pharmaceutical compositions especially pharmaceutical compositions having enkephalinase inhibiting activity, analgesic or antihypertensive activity. 
     The pharmaceutical compositions according to the invention are those suitable for enteral, such as oral or rectal, transdermal and parenteral administration to mammals, including man, for the treatment of disorders such as pain or hypertension, comprising an effective amount of a pharmacologically active compound of the invention or a pharmaceutically acceptable salt thereof, alone or in combination with one or more pharmaceutically acceptable carriers. 
     The pharmacologically active compounds of the invention are useful in the manufacture of pharmaceutical compositions comprising an effective amount thereof in conjunction or admixture with excipients or carriers suitable for either enteral or parenteral application. Preferred are tablets and gelatin capsules comprising the active ingredient together with a) diluents, e.g. lactose, dextrose, sucrose, mannitol, sorbitol, cellulose and/or glycine; b) ubricants, e.g. silica, talcum, stearic acid, its magnesium or calcium salts and/or polyethyleneglycol; for tablets also c) binders,e,g, magnesium aluminum silicate, starch paste, gelatin, tragacanth, methylcellulose, sodium carboxymethylcellulose and/or polyvinylpyrrolidone; if desired, d) disintegrants, e.g. starches, agar, alginic acid or its sodium salt, or effervescent mixtures; and/or e) absorbents, colorants, flavors and sweeteners. Injectable compositions are preferably aqueous isotonic solutions or suspensions, and suppositories are advantageously prepared from fatty emulsions or suspensions. Said compositions may be sterilized and/or contain adjuvants, such as preserving, stabilizing, wetting or emulsifying agents, solution promoters, salts for regulating the osmotic pressure and/or buffers. In addition, the compositions may also contain other therapeutically valuable substances. Said compositions are prepared according to conventional mixing, granulating or coating methods, respectively, and contain about 0.1 to 75%, preferably about 1 to 50%, of the active ingredient. 
     Suitable formulations for transdermal application include an effective amount of a compound of the invention with carrier. Advantageous carriers include absorbable pharmacologically acceptable solvents to assist passage through the skin of the host. Characteristically, transdermal devices are in the form of a bandage comprising a backing member, a reservoir containing the compound, optionally with carriers, optionally a rate controlling barrier to deliver the compound to the skin of the host at a controlled and predetermined rate over a prolonged period of time, and means to secure the device to the skin. 
     A unit dosage for a mammal of about 50 to 70 kg may contain between about 5 and 100 mg of the active ingredient. The dosage of active compound is dependent on the species of warm-blooded animal (mammal), the body weight, age and individual condition, and on the form of administration. 
     The following examples are intended to illustrate the invention and are not to be construed as being limitations thereon. Temperatures are given in degrees Centigrade. If not mentioned otherwise, all evaporations are performed under reduced pressure, preferably between about 15 and 100 mm Hg. optical rotations are measured at room temperature and in methanol at a 1% concentration unless otherwise indicated. 
     The prefixes R* and S* as used herein, e.g. when referring to a 2,4-disubstituted-4-carboxybutyryl grouping (a 2,4-disubstituted glutaryl grouping) or derivatized form thereof, are used to indicate the relative configuration of the two asymmetric centers in the racemic form. The prefixes R and S are used to indicate the absolute configuration at each asymmetric center in the enantiomeric form. 
     EXAMPLE 1 
     A solution of 1.0 g of O-benzyl-(L)-serine and 1.0 g of trans-(S,S)-2,4-dibenzylglutaric anhydride in 15 ml of pyridine and 15 ml of methylene chloride is stirred at room temperature overnight. The mixture is concentrated, the residue dissolved in ether-ethyl acetate (1:1) and the solution is washed with lN hydrochloric acid, saturated sodium chloride, dried over magnesium sulfate and concentrated. The residue is washed with cold ether and the solid is collected to yield N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-O-benzyl-(L)-serine, melting at 149°-151°; [alpha] D  =+25.2°. 
     The starting material is prepared as follows: 
     6.9 g of 2,4-Dibenzylglutaric acid (Acta Chem. Scand. 1958, 314) is refluxed in 50 ml of acetyl chloride for 3 hours, concentrated, diluted with 25 ml of toluene and evaporated to give a mixture of meso (cis)- and racemic (trans)-2,4-dibenzylglutaric anhydride. The residue is dissolved in 8.5 ml of toluene and 1.5 ml of triethylamine and heated to 50° until all the solid dissolves. The solution is left to stand overnight. The solid is collected to yield the trans-2,4-dibenzylglutaric anhydride melting at 153°-155°. Heating under reflux with dioxane, water (1:1) overnight yields racemic (R*, R*)-di-benzylglutaric acid melting at 150°-152°. 
     The racemic trans-2,4-dibenzylgluratic anhydride can also be isolated directly from the mixture of meso cis- and racemic trans-2,4-dibenzylglutaric anhydride by fractional crystallization with toluene. The mother liquors are then concentrated and upon standing crystallization occurs. After stirring with cyclohexane the solid is collected to yield the (cis)-meso-2,4-dibenzylglutaric anhydride melting at 55°-57°. 
     The (S,S)-2,4-dibenzylglutaric anhydride [mp 172°-174°; [alpha] D  =-19.1° (c=1 in CHCl 3 )]is prepared similarly by refluxing (S,S)-2,4-dibenzylglutaric acid in acetyl chloride for 3 hours, concentrating the mixture and recrystallizing from toluene. 
     The chiral (S,S)-2,4-dibenzylglutaric acid is prepared as follows: To 5.0 g of (R*,R*)-2,4-dibenzylglutaric acid in 20 ml of isopropanol is added 0.81 g of triethylamine and the mixture is stirred for 20 minutes. To this mixture is added 0.97 g of d(+)-alpha-methylbenzylamine in 20 ml of isopropanol and the solution is stirred overnight. The solid is collected and recrystallized twice from isopropanol to yield (S,S)-2,4-dibenzylglutaric acid as the d(+)-alpha-methylbenzylamine salt melting at 201°-203°; [alpha] D  =-20.4° (c=1 in methanol). To a warm solution of the above salt in 70 ml of water and 30 ml of ethanol is added 1 ml of concentrated hydrochloric acid. After standing 24 hours the solid is collected, washed with water and dried to yield (S,S)-2,4-dibenzylglutaric acid melting at 150°-152°; [alpha] D  =+8.9° (c=2.0 in methanol). 
     EXAMPLE 2 
     The following compounds are prepared according to the methods illustrated by the previous example. 
     a) N-[(R*,R*)-2,4-dibenzyl-4-carboxybutyryl]glycine, isolated as the disodium salt, m.p. 260°-263°, using racemic (trans)-2,4-dibenzylglutaric acid as starting material. 
     The disodium salt is prepared by dissolving the diacid in methanol - water (2:1), adding two molar equivalents of 1.0N sodium hydroxide, evaporating the solution to dryness, suspending the residue in ethanol, and drying the resulting solids under high vacuum at about 50°. 
     b) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-leucine, m.p. 129°-131°. 
     c) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-phenylalanine isolated as the disodium salt, m.p. above 300°, [alpha] D  =+20.8°. 
     d) N-[S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-tyrosine isolated as the disodium salt, m.p. above 300°, [alpha] D  =+24.9°. 
     e) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-tryptophane isolated as the disodium salt, m.p. above 300°, [alpha] D  =+11.0°. 
     f) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-homophenylalanine, m.p. 165°-167°, [alpha] D  =+12.9°. 
     g) N-(S,S)-2,4-dibenzyl-4-carboxybutyryl]-S-benzyl-(L)-cysteine, m.p. 134°-136°, [alpha] D  =+55.3°. 
     h) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-S-(2-pyridylmethyl)-(L)-cysteine,m.p. 79°-82°. 
     i) N-[(R*,S*)-dibenzyl-4-carboxybutyryl]-S-benzyl-(L)-cysteine. 
     EXAMPLE 3 
     According to procedures illustrated in the previous example are also prepared: 
     a) N-[(R*,R*)-2,4-di-(phenethyl)-4-carboxybutyryl]-O-benzyl-(L)-serine; 
     b) N-[(R*,R*)-2,4-di-(phenethyl)-4-carboxybutyryl]-S-(2-pyridylmethyl)-(L)-cysteine. 
     The starting material is prepared as follows: 
     5.0 g of (R*,R*)-2,4-Di(phenethyl)-glutaric acid is refluxed in 50 ml of acetyl chloride for 3 hours, concentrated, diluted with toluene and evaporated to give trans-(R*,R*)-2,4-di(phenethyl)-glutaric anhydride. 
     The mixture of isomers of 2,4-di-(phenethyl)glutaric acid are prepared following the general procedure described in Acta Chem. Scand. 1958, 314. The reaction mixture is recrystallized from cyclohexane to yield (R*,S*)-2,4-di-(phenethyl)glutaric acid melting at 129°-132°. The mother liquor is concentrated and the residue is recrystallized twice from cyclohexane:toluene (3:2) to yield (R*,R*)-2,4-di(phenethyl)-glutaric acid melting at 95°-105°. 
     EXAMPLE 4 
     A suspension of 0.5g of N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-leucine and 0.5g of 5% Rh/C in 10 ml of ethanol and 10 ml of water is hydrogenated for 36 hours at 3 atmospheres pressure (50 psi). The mixture is filtered through celite and concentrated. The colorless oil is treated with 1.0 N sodium hydroxide in methanol and concentrated to yield N-[(S,S)-2,4-di-(cyclohexylmethyl)-4-carboxybutyryl]-(L)-leucine. 
     EXAMPLE 5 
     A solution of 3.3g of O-benzyl-(S)-serine and 1.8 g of sodium carbonate in 30 ml of water at 0° is added to 2.2 g of 4-ethoxycarbonyl-(S,S)-2,4-dibenzylbutyryl chloride and the mixture is stirred at room temperature for 4 hours. The mixture is extracted with ether, and the aqueous layer is acidified with 2N hydrochloric acid. The acidic solution is extracted with ethyl acetate, washed with saturated brine, dried (magnesium sulfate), filtered and concentrated to yield N-[4-ethoxycarbonyl-(S,S)-2,4-di-benzylbutyryl]-O-benzyl-(L)-serine. 
     The starting material is prepared as follows: 4.0 g of (S,S)-2,4-dibenzylglutaric anhydride is refluxed in 40 ml of ethanol:toluene (3:2) overnight. The reaction mixture is concentrated to yield 4-ethoxycaronyl-(S,S)-2,4-dibenzylbutyric acid as an oil. Oxalyl chloride (3.5 ml) is added to the solution of 4.5 g of 4-ethoxycarbonyl(S,S)-2,4-dibenzylbutyric acid in 10 ml of methylene chloride. The mixture is stirred at room temperature overnight and evaporated to yield 4-ethoxycarbonyl-(S,S)-2,4-dibenzylbutyryl chloride, which is used as such without further purification. 
     EXAMPLE 6 
     4-(Pivaloyloxymethoxycarbonyl)-2,4-(R*,R*)-dibenzylbutyryl chloride (1.2 g) in 10 ml of methylene chloride is added slowly to a solution of 0.60 g of (L)-leucine benzyl ester and 0.30 ml of triethylamine in 20 ml of methylene chloride. The reaction is stirred overnight at room temperature. The solution is washed with 2 N hydrochloric acid, then with saturated sodium bicarbonate, dried over magnesium sulfate, filtered and concentrted to give N-[4-pivaloyloxymethoxycarbonyl-(R*,R*)-2,4-dibenzylbutyryl]-L-leucine benzyl ester. 
     The starting material is prepared as follows: 
     A mixture of 4.0 g of 2,4-trans-dibenzylglutaric anhydride and 1.5 ml of benzyl alcohol in 15 ml of toluene is stirred at 80° for 16 hours to give 4-(benzyloxycarbonyl)-(R*,R*)-2,4-dibenzylbutyric acid. 
     The above acid (3.2 g) is treated with 3.8 ml of 2.1 N potassium hydroxide. The solution is evaporated. Toluene (100 ml) is added and the mixture is evaporated to give potassium 4-(benzyloxycarbonyl)-(R*,R*)-2,4-di-benzylbutyrate. 
     To chloromethyl pivalate (1.13 g) in 25 ml of acetone is added sodium iodide (1.11 g). The reaction is stirred at room temperature for 3 hours. The reaction mixture is filtered and the filtrate is evaporated. To the residue in 25 ml of dimethylformamide is added potassium 4-(benzyloxycarbonyl)-(R*,R*)-2,4-dibenzylbutyrate (3.3 g) in 25 ml of dimethylformamide. The reaction mixture is stirred at room temperature for 18 hours and then evaporated. The residue is dissolved in 150 ml of ether and washed with 3×50 ml of 10% aqueous sodium bicarbonate and 3×50 ml of saturated aqueous sodium chloride. The organic layer is dried over magnesium sulfate and evaporated to give pivaloyloxymethyl 4-(benzyloxycarbonyl)-2,4-(R*,R*)-dibenzylbutyrate. 
     A solution of 2.5 g of pivaloyloxymethyl 4-(benzyloxycarbonyl)-(R*,R*)-2,4-dibenzylbutyrate in 75 ml of ethanol is hydrogenated at atmospheric pressure in the presence of 0.2 g of 5% palladium on carbon. The reaction is filtered and evaporated to give 4-(pivaloyloxymethoxycarbonyl)-2,4-(R*,R*)-dibenzylbutyric acid. 
     To 1.8 g of the above acid in 30 ml of methylene chloride at room temperature is added 1.2 ml of oxalyl chloride. The reaction is stirred at room temperature for 2.3 hours and then evaporated to give 4-(pivaloyloxymethoxycarbonyl)-2,4-(R*,R*)-dibenzylbutyryl chloride. 
     EXAMPLE 7 
     0.85 g of N-[4-pivaloyloxymethoxycarbonyl-(R*,R*)-2,4-dibenzylbutyryl]-(L)-leucine benzyl ester in 20 ml of ethanol is hydrogenated at atmospheric pressure in the presence of 0.1 g of 5% palladium on carbon. The reaction is filtered and evaporated to give N-[4-pivaloyloxymethoxycarbonyl-(R*,R*)-2,4-dibenzylbutyryl]-(L)-leucine. 
     EXAMPLE 8 
     a) To a solution of 0.012 mole of 1,1&#39;-carbonyldiimidazole in 20 ml of methylene chloride at 0° is added a solution of 0.01 mole of (S,S)-4-ethoxycarbonyl-2,4-di-benzylbutyric acid in 20 ml of methylene chloride. After 1 hour 0.01 mole of (S)-benzylcysteine in 10 ml of pyridine is added dropwise over a period of 15 minutes. The reaction mixture is stirred at room temperature overnight. The reaction mixture is evaporated to dryness. The residue is dissolved in 75 ml of methylene chloride and washed with 2×25 ml of 2N aqueous hydrochloric acid. The organic layer is dried over magnesium sulfate and evaporated to give after recrystallization from ether N-[4-ethoxycarbonyl-(S,S)-2,4-dibenzylbutyryl]-S-benzyl-(L)-cysteine. 
     b) Similarly prepared is N-[4-ethoxycarbonyl-(S,S)-2,4-dibenzylbutyryl]-O-benzyl-(L)-serine. 
     EXAMPLE 9 
     a) A solution of 0.5 g of (S,S)-2,4-dibenzylglutaric anhydride and 0.82 g of O-benzyl-(L)-serine 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester in 10 ml of methylene chloride is stirred at room temperature overnight. The solution is diluted with ether, washed with 1N hydrochloric acid, water, dried (Na2S04), filtered and concentrated to give N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-O-benzyl-(L)-serine 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester melting at 55°-58°; [α] D  =+2.2°. 
     The starting material is prepared as follows: 
     A solution of 1.lg of N-carbobenzoxy-O-benzyl-(L)-serine, 0.88 g of diacetone-D-glucose, 0.74 g of 1-(3-di-methylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.41 g of 4-dimethylaminopyridine in 20 ml of methylene chloride is stirred at room temperature overnight. The mixture is concentrated, ethyl acetate is added and washed with 1N hydrochloric acid, water, saturated sodium bicarbonate, dried (Na 2  SO 4 ), filtered and concentrated. The residue is chromatographed on silica eluting with ethyl acetate-methylene chloride (1:4) to give N-carbobenzoxy-0-benzyl-(L)-serine 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester. 
     To the above ester is added 5% palladium on carbon and 10 ml of ethanol. The suspension is hydrogenated at atmospheric pressure for 1 hour. The catalyst is removed by filtration through celite. The filtrate is concentrated to give O-benzyl-(L)-serine 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester. 
     Prepared similarly are: 
     b) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-homophenylalanine 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester melting at 63°-65°; [alpha] D  =-10.6°; 
     c) monoesters of N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-O-benzyl-(L)-serine in which the serine carboxy group is esterified as: 
     1. The 1,2:3,4-di-O-isopropylidene D-galactopyranos-6-yl ester; 
     2. The 2,3-O-isopropylidene-D-ribono-(1,4-lactone)-5-yl ester; 
     3. The 2,3:5,6-di-O-cyclohexylidene-D-mannofuranos-1-yl ester; 
     4. The 2,3-O-cyclohexylidene-D-ribono-(1,4-lactone)-5-yl ester; 
     5. The 1-methyl-2,3,-O-isopropylidene-β-D-ribofuranos-5-yl ester; 
     6. The 4-pyridylmethyl ester; 
     7. The 2,3:4,6-di-O-isopropylidene-L-sorbofuranos-1-yl ester; 
     8. The D-ribono(1,4-lactone)-5-yl ester. 
     The above esters are prepared using the alcohols which are either commercially available, known in the literature or prepared according to known methods, e.g. 2,3:5,6-di-0-cyclohexylidene-alpha-D-mannofuranose, J. Chem. Soc. 853 (1959); 2,3-O-isopropylidene-D-ribono-1,4-lactone, Can. J. chem. 1720 (1958); 2,3:4,6-di-O-isopropylidene-alpha-L-sorbofuranose, Biochemistry 26, 201 (1971); 1-methyl-2,3-O-isopropylidene-D-ribofuranoside; 1,2:5,6-di-O-isopropylidene-D-glucofuranose; 1,2:3,4-di-O-isopropylidene-D-galactopyranose. 
     EXAMPLE 10 
     To a solution of 0.5 g of (L)-homophenylalanine 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester, 0.51 g of 4-[(2,2-dimethyl-1,3-dioxolan-4-yl)-methoxycarbonyl]-(S,S)-2,4-dibenzylbutyric acid is added 0.23 g of 1-(3-dimethylminopropyl)-3-ethylcarbodiimide hydrochloride. The solution is stirred overnight. The solution is diluted with ethyl acetate, washed in sequence with 1N hydrochloric acid, water, saturated sodium bicarbonate, water, dried (Na 2  SO 4 ), filtered and concentrated. The residue is flash chromatographed on silica gel eluting with ethyl acetate-methylene chloride (1:4) giving N-{4-[(2,2-dimethyl-1,3-dioxolan-4-yl)-methoxycarbonyl]-(S,S)-2,4-dibenzylbutyryl}-(L)-homophenylalanine 1,2:5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester melting at 48°-50°. 
     The starting material is prepared as follows: 
     A solution of 1.0 g of (S,S)-2,4-dibenzylglutaric anhydride and 0.54 g of 4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane in 10 ml of toluene is refluxed overnight. The solution is washed with water, dried (Na 2  SO 4 ), filtered and concentrated to give 4-[(2,2-dimethyl-1,3-dioxolan-4-yl)-methoxycarbonyl]-(S,S)-2,4-dibenzylbutyric acid as a viscous oil. 
     EXAMPLE 11 
     A solution of 4.5 g of S-benzyl-(L)-cysteine methyl ester and 2.8 g of (S,S)-2,4-dibenzylglutaric anhydride in 25 ml of pyridine and 25 ml of methylene chloride is stirred at room temperature overnight. The mixture is concentrated, the residue is dissolved in ether and the solution is washed with lN hydrochloric acid, saturated sodium chloride, dried over magnesium sulfate, concentrated, to yield N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-S-benzyl-(L)-cysteine methyl ester (oil). 
     EXAMPLE 12 
     A solution of 2.1 g of N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-S-benzyl-(L)-cysteine methyl ester 0.60  g of 2-aminopyridine and 1.2 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride in 25 ml of methylene chloride is stirred at room temperature overnight. The mixture is concentrated, ethyl acetate is added and washed with water, sodium bicarbonate, dried (Na 2  SO 4 ), filtered and concentrated. The residue is chromatographed on silica gel eluting with ethyl acetatemethylene chloride (1:9) to give N-[4-(2-pyridylaminocarbonyl)-(S,S)-2,4-dibenzylbutyryl]-S-benzyl-(L)-cysteine methyl ester (oil). 
     EXAMPLE 13 
     A solution of 0.3 g of N-[4-(2-pyridylaminocarbonyl)-(S,S)-2,4-dibenzylbutyryl]-S-benzyl-(L)-cysteine methyl ester and 1 ml of 1N sodium hydroxide in 2 ml of methanol is stirred at room temperature overnight. To the solution is added 1.1 ml of 1N hydrochloric acid. The solution is concentrated, diluted with water, the solid is collected and dried under high vacuum to give N-[4-(2-pyridylaminocarbonyl)-(S,S)-2,4-dibenzylbutyryl]S-benzyl-(L)-cysteine, melting at 75-80°; [alpha] D  =+22.9°. 
     EXAMPLE 14 
     4-[1,2:3,4-di-O-isopropylidene-D-galactopyranos-6-yl oxycarbonyl]-(S,S)-2,4-dibenzylbutyric acid is condensed with O-benzyl-(L)-serine benzyl ester using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide/triethylamine to give N-[4-(1,2:3,4-di-O-isopropylidene-D-galoctopyranos-6-yloxycarbonyl)-(S,S)-2,4-dibenzylbutyryl]-O-benzyl-(L)-serine benzyl ester. Treatment with hydrogen and 5% palladium on charcoal in ethanol at room temperature yields N-[4-(1,2:3,4-di-O-isopropylidene-D-galactopyranos-6-yloxycarbonyl)-(S,S)-2,4-dibenzylbutyryl]-O-benzyl-(L)-serine. 
     The starting material is prepared as follows: 
     The solution of 1 g of (S,S)-2,4-dibenzylglutaric anhydride and 1.06 g of 1,2,3,4-di-O-isopropylidene-D-galactopyranose in 10 ml of toluene is refluxed overnight. The solution is diluted with toluene, washed with water, dried (Na 2  SO 4 ), filtered, and concentrated to give 4-[1,2:3,4-di-O-isopropylidene-D-galactopyranos-6-yloxycarbonyl]-(S,S)-2,4-dibenzylbutyric acid as a viscous oil. 
     EXAMPLE 15 
     The solution of 320 mg of N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-O-benzyl-(L)-serine 1,2,5,6-di-O-isopropylidene-D-glucofuranos-3-yl ester (compound of Example 9a) in 9ml of 80% aqueous acetic acid is stirred at room temperature for 24 hours. The mixture is concentrated. Residual acetic acid is removed by addition of toluene and concentrating the solution. The N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-O-benzyl-(L)-serine 1,2-O-isopropylidene-D-glucofuranos-3-yl ester is obtained. 
     EXAMPLE 16 
     According to methods similar to those described in the previous examples are prepared: 
     (a) N-[(S,S)-2,4-di-(p-chlorobenzyl)-4-carboxybutyryl]-O-benzyl-(L)-serine; 
     (b) N-[(S,S)-2,4-di-(p-trifluoromethylbenzyl)-4-carboxybutyryl]-(L)-homophenylalanine; 
     (c) N-[(S,S)-2,4-di-(3-thienylethyl)-4-carboxybutyryl]-(L)-homophenylalanine; 
     (d) N-[(S,S)-2,4-di-(3-pyridylmethyl)-4-carboxybutyryl]-O-benzyl-(L)-serine; 
     (e) N-[(S,S)-2,4-di-(2-naphthylethyl)-4-carboxybutyryl]-S-benzyl-(L)-cysteine. 
     (f) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-glycine, m.p. 61°-63°, [alpha] D  =+22.0°; 
     (g) N-[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)arginine, m.p. 140°-142°, [alpha] D  =+25.2°; 
     (h) N alpha  -[(S,S)-2,4-dibenzyl-4-carboxybutyryl-N epsilon  -carbobenzyloxy-(L)-lysine, m.p. 160°-170° dec, alpha] D  =+22.8°; 
     (i) N alpha  -[(S,S)-2,4-dibenzyl-4-carboxybutyryl]-(L)-lysine, m.p. 118°-128°, [alpha] D  =+30.6°, prepared by hydrogenolysis of compound h) using hydrogen in the presence of palladium on charcoal. 
     EXAMPLE 17 
     According to the methods described in the previous examples are also prepared: 
     a) N-[4-aminocarbonyl-(S,S)-2,4-dibenzylbutyryl]-(L)-homophenylalanine, m.p. 212°-214°; [alpha] D  =+17.4°; 
     b) N-[4-(p-chloroanilinocarbonyl)-S,S)-2,4-dibenzylbutyryl]-S-benzyl-(L)-cysteine, m.p. 185°-189°; [alpha] D  =+18.1°; 
     c) N-[4-(anilinocarbonyl)-(S,S)-2,4-dibenzylbutyryl]-S-benzyl-(L)-cysteine, m.p. 108°-110°; [alpha] D  =+9.2°; 
     d) N-[4-(butylaminocarbonyl)-(S,S)-2,4-dibenzylbutyryl]-S-benzyl-(L)-cysteine, m.p. 68°-72°; [alpha] D  =-25.3°; 
     e) N-[4-(3-phenylpropylaminocarbonyl)-(S,S)-2,4-dibenzylbutyryl]-S-benzyl-(L)-cysteine, m.p. 120°-122°. 
     EXAMPLE 18 
     Preparation of an injectable formulation containing 25 mg of the active ingredient per 5 ml of solution: 
     
         ______________________________________                                    
Formula                                                                   
______________________________________                                    
N-[(S,S)-2,4-dibenzyl-4-carboxy-                                          
                        25.0    g                                         
butyryl]-O-benzyl-(L)-serine                                              
Sodium bicarbonate      5.5     g                                         
Propylparaben           1.0     g                                         
Water for injection q.s.                                                  
                        5000.0  ml                                        
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     The active ingredient, sodium bicarbonate and preservative are dissolved in 3500 ml of water for injection and the solution is diluted to 5000 ml. The solution is filtered through a sterile filter and filled into injection vials under sterile conditions each vial containing 5 ml of the solution. 
     EXAMPLE 19 
     Preparation of 10,000 capsules each containing 20 mg of the active ingredient. 
     
         ______________________________________                                    
Formula:                                                                  
______________________________________                                    
N-[(S,S)-2,4-dibenzyl-4-carboxy-                                          
                         200.00  g                                        
butyryl]-O-benzyl-(L)-serine                                              
1,2:5,6-di-O-isopropylidene-D-gluco-                                      
furanos-3-yl ester                                                        
Lactose                  1,790.0 g                                        
Magnesium stearate       10.0    g                                        
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     Procedure 
     The powders are passed through a screen with openings of 0.6 mm. then the drug substance is placed in a suitable mixer and mixed with the lactose and magnesium stearate until homogeneous. No. 3 capsules are filled with 200 mg using a capsule filling machine.